5 HIAA

FIGURE 3-27 Three-dimensional chromatogram for oxidizable biological compounds at a multichannel amperometric detection system, consisting of an array of 16 carbon-paste electrodes held at different potentials. AA = ascorbic acid NE = norepinephrine DOPAC = 3,4-dihydroxyphenylacetic acid 5-HIAA = 5-hydroxyindole-3-acetic acid DA = dopamine HVA = homovanillic acid. (Reproduced with permission from reference 68.)... 

HT is metabolised primarily by MAO to 5-hydroxyindoleacetic acid (5-HIAA) (Fig. 9.4). In vitro, 5-HT is the preferred substrate for the MAOa, rather than the MAOb isoenzyme (see Chapter 8) and this appears to be the case in vivo since MAOa, but not MAOb, knock-out mice have increased concentrations of 5-HT in the brain. Obviously, because of its indole nucleus, 5-HT is not a substrate for the enzyme COMT which metabolises the catechol derivatives, dopamine and noradrenaline. However, other metabolic products of 5-HT are theoretically possible and one, 5-hydroxytryptophol,... 

The comparatively straightforward link between 5-HT and its primary metabolite, 5-HIAA, encouraged many researchers to use changes in the ratio of tissue concentrations of 5-HIAA and 5-HT as an index of the rate of release of 5-HT ex vivo. However, it has been clear for some time that the majority of 5-HT is metabolised in the cytoplasm by MAO before it is released from 5-HT nerve terminals. Consequently, the reliability of the 5-HIAA 5-HT ratio as an index of transmitter release is rather dubious, although it could be used as an acceptable measure of MAO activity. In any case, the development of in vivo microdialysis means that changes in the concentration of extracellular 5-HT can now be monitored directly which, under drug-free conditions, provides a far more reliable indication of any changes in the rate of release of 5-HT. 

So far, evidence for abnormal peripheral (Elliott 1992) or central (Horton 1992) monoamine function in depression is equivocal, and no consistent biochemical markers have emerged to provide a firm link between the two (Table 20.2). One widely cited finding is that subjects who have attempted violent suicide form a neurochemically distinct group because the concentration of the 5-HT metabolite, 5-HIAA, in their CSF is lower than normal, suggesting that a deficit in 5-HT release is associated with suicide... 

Asberg, M, Traskman, L and Thoren, P (1976) 5-HIAA in the cerebrospinal fluid a biological chemical suicide predictor. Arch. Gen. Psychiatry 33 1193-1197. 

The problem of selectivity is the most serious drawback to in vivo electrochemical analysis. Many compounds of neurochemical interest oxidize at very similar potentials. While this problem can be overcome somewhat by use of differential waveforms (see Sect. 3.2), many important compounds cannot be resolvai voltammetrically. It is generally not possible to distinguish between dopamine and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) or l tween 5-hydroxytryptamine (5-HT) and 5-hydroxyindolacetic acid (5-HIAA). Of even more serious concern, ascorbic acid oxidizes at the same potential as dopamine and uric acid oxidizes at the same potential as 5-HT, both of these interferences are present in millimolar concentrations... 

Dr. Gibb s hypothesis regarding dopamine involvement, we thought that perhaps MBDB would not be neurotoxic because of a lack of effect on dopamine. But, in fact, it is neurotoxic as well, measured by whole-brain serotonin 5-HIAA and tritiated paroxetine binding sites. It is perhaps two-thirds the toxicity, on a molecular weight basis, of MDMA, but it is toxic. 

QUESTION Did you measure tryptophan hydroxylase or just the 5-HT/5-HIAA depletion ... 

ANSWER We used it in the 20 mg/kg twice a day for a 4-day regimen with MDMA, and then corrected for molecular weight and used an equimolar dose of MBDB, sacrificed the animals 2 weeks later, and then measured. We used basically HPLC and used serotonin and 5-HIAA from one hemisphere and then measured tritiated pyroxetine from the other hemisphere. And we got something like 60 percent depletion of serotonin, and the pyroxetine binding site decreased by about 60 percent. With MBDB it was decreased by about 40 percent. It was a clear and significant decrease, but not quite to the extent that we had. But we have not looked at tryptophan hydroxylase. 

When administered in doses higher than 12 mg/kg/day, depletions of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) last up to 6 months after cessation of drug treatment (Harvey and McMaster 1975 Harvey et al. 1977 Clineschmidt et al. 1978 Steranka and Sanders-Bush 1979 Schuster et al. 1986 Kleven et al. 1988). Other long-lasting effects of fenfluramine include a decrease in 5-HT uptake sites (Schuster et al. 1986) and tryptophan hydroxylase activity (Steranka and Sanders-Bush 1979). 

In 1985, Seiden and his coworkers reported that 3,4-methylenedioxy-amphetamine (MDA) caused a decrease in brain 5-HT and 5-HIAA concentrations 5-HT uptake was also compromised (Ricaurte et al. 1985). We compared the effects of the methylenedioxy derivatives of METH and amphetamine on the serotonergic and dopaminergic parameters previously demonstrated as altered by METH administration (Stone et al. 1986). 

Multiple doses of MDMA or MDA resulted in a further decline in TPH activity (figure 4). In contrast to METH, however, neither MDA nor MDMA altered neostriatal TH activity. The decrease in TPH activity was accompanied by a dramatic decrease in 5-HT and 5-HIAA concentrations these changes in TPH activity and in 5-hydroxyindole content also occurred in other serotonergic terminal areas such as the hippocampus and cerebral cortex. Both neostriatal DA and homovanillic acid (HVA) were initially elevated 3 hours after a single dose of MDMA, but had returned to normal... 

Subsequent experiments were designed to eharacterize further the response of the serotonergie system to MDMA. When a single low dose (5 mg/kg) of MDMA was administered, there was an initial decrease in TPH activity and concentrations of 5-HT and 5-HIAA. These serotonergic parameters... 

The possible role of DA in the MDMA-indueed alterations of the serotonergie system was then examined. Teehniques previously used in studying the role of DA in the METH-indueed neuroehemieal effeets were employed. When DA synthesis was inhibited with MT, the effeet of multiple doses of MDMA on TPH activity (figure 6) and eoneentrations of 5-HT and 5-HIAA was attenuated. The degree of proteetion with MT seemed to be a funetion of the size and number of doses of MDMA used as well as a funetion of the serotonergie parameter that was measured. 

FIGURE 2. The effects of single and multiple injections of MDMA on the content of serotonin (5-HT) and 5-HIAA and the density of 5-HT uptake sites in rat frontal cerebral cortex... 

In more recent studies, it has also demonstrated that administration of 2.5 or 10 mg/kg MDMA twice daily for 4 consecutive days resulted in neurotoxic effects in rhesus monkeys, with decreases in the density of serotonin uptake sites occurring at the higher dose (Johannessen et al. 1988). The neurotoxic effects of MDMA observed in primates included reductions in the content of serotonin and 5-HLAA and marked reductions in the cerebrospinal (CSF) concentrations of 5-HIAA levels that were observed following drug administration. These findings and other reports of neurotoxic effects of MDMA in primates (Ricaurte et al. 1988) raise serious concerns for its potential hazard in humans. 

Since the neurotoxic effects of drugs such as parachloroamphetamine on serotonin neurons can be prevented by serotonin uptake blockers (Ross 1976 Sanders-Bush and Steranka 1978). the possibility that serotonin uptake carrier protein was likewise involved in the neurotoxic effects of MDMA was investigated. As shown in figure 4, pretreatment of rats with the seleetive serotonin uptake blocker citalopram (10 ml/kg), prior to each injection of 10 mg/kg MDMA, resulted in nearly complete protection against the neurotoxic effects of MDMA. Citalopram-pretreated rats exhibited only a 15 pereent decrease in serotonin uptake sites. No significant alterations in the eontent of serotonin and 5-HIAA were observed following MDMA treatment, in eomparison with 60 to 80 percent reductions in the serotonergie parameters observed in rats treated with an identical dose of MDMA alone. 

Effects of MDMA on Serotonin and 5-HIAA Content and [ HJParoxetine-Labeled Serotonin Uptake Sites in Discrete Regions of Rat Brain... 

This chapter will review some recently completed studies on the long-term effects of MDMA in nonhuman primates. The goals of these studies were to (1) determine if the neurotoxic effects of MDMA, which have been well documented in the rodent (see below), generalize to the primate (2) compare the relative sensitivity of primates and rodents to the neurotoxic effects of MDMA (3) ascertain if the toxic effects of MDMA in the monkey are restricted to nerve fibers (as they are in the rat), or if they involve cell bodies as well (4) evaluate how closely toxic doses of MDMA in the monkey approximate those used by humans and (5) examine whether 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF) can be used to detect MDMA-induced serotonergic damage in the CNS of primates. Before presenting the results of these studies, previous results in the... 

TABLE 2. Decreased concentration of 5-HIAA in the monkey brain 2 weeks... 

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